If you're doing this repair on your own personal amp, the 0805 sized resistors would likely be OK (if they are long enough to make contact with the solder pads).

If this is an amp that you're repairing for someone else and you're charging them for the repair, order the correct part. If the customer takes it to another shop and they see that someone has used the wrong size component, they're likely to tell the customer and that's likely to tarnish your reputation (even though the smaller part is large enough to do the job).